1. Field of the Invention
This invention relates to an information recording apparatus for recording information onto an information recording medium and, more particularly, to an optical-disk recording apparatus for recording the information onto an optical disk, such as CD-R, CD-RW, DVD-R, DVD-RW, while it is being rotated.
2. Description of the Related Art
Conventionally, almost all the optical-disk recording apparatus for recording the information onto a recordable optical disk, such as CD-R, CD-RW, DVD-R, DVD-RW, each controls a rotational speed of a spindle motor for rotating the optical disk in such a way that a liner velocity at which an optical spot for recording the information optically scans a track having a shape of a groove that is formed beforehand on the optical disk becomes virtually constant (Constant Linear Velocity, hereinafter referred to as “CLV”) when recording the information. However, recently there have appeared some optical-disk recording apparatuses each of which records the information in such a way that an angular velocity of an optical disk being recorded is controlled to be virtually constant (Constant Angular Velocity, hereinafter referred to as “CAV”). Merits associated with a change of the disk rotational speed at the time of recording from a CLV scheme to a CAV scheme are enumerated as follows: since it is not necessary to vary the disk rotational speed even when the recording position on the disk is changed, settling time of the rotational speed is unnecessary; there is no increase in power consumption caused by acceleration and deceleration when the rotational speed is varied; etc.
When recording the information at CAV, the linear velocity varies according to the radius of the recording position on the disk, and consequently the data transfer rate during the recording is changed. Therefore, several circuits, such as an encoder circuit for generating recording data and a recording strategy circuit for determining laser irradiation timing necessary in the recording, are required to be capable of varying an operating speed during the recording; therefore, the clock signal serving as a reference of the operation of each circuit (hereinafter referred to as the “recording-system clock”) must be capable of being varied.
Next, a method for performing CAV recording will be explained. In order to record the information at CAV actually, it is necessary to rotate the disk at CAV. To achieve this, all that is necessary is just to add a sensor for detecting the rotational speed, such as an FG, on the spindle motor to obtain a signal of a frequency proportional to the rotational speed and control the rotational speed of the spindle motor so that the frequency of this rotational speed signal becomes approximately constant. Concretely, a frequency and/or a phase of the rotational speed signal are compared to those of a fixed standard frequency signal, and the rotational speed of the spindle motor is so controlled that this difference becomes as small as possible. At this time, the frequency of the rotational speed becomes approximately constant and the disk rotates at CAV.
When the disk is being rotated at CAV, the data recording density varies according to the recording radius, and as a result, a recording-system clock frequency varies. Here, as described above, the CD standard stipulates that a ratio between the carrier frequency and the recording-system clock frequency shall be a constant value regardless of the disk rotational speed. This relation also stands even when the spindle motor is rotating at CAV.
Note here that even when the disk is being rotated at CAV, it is possible to detect the carrier frequency and determines the recording-system clock frequency from this value. Concretely, all that is necessary is just to generate a signal having the above-mentioned specified frequency ratio with reference to the carrier frequency using a PLL circuit etc. and set it as the recording-system clock. In the conventional technology, the CAV recording is realized by controlling the spindle motor and the recording-system clock in this way.
In the case of realizing the CAV recording by the above-mentioned method, the processing is such that a carrier signal is extracted from a wobble signal that is reproduced from the disk via a pick-up, and based on this signal the recording-system clock is generated by a clock generating system such as the PLL circuit. Therefore, the recording-system clock is affected by the disk, the CAV control system for rotating the disk, a wobble-signal reproduction system, a carrier-signal extraction system, a clock generation system, etc. Therefore, in order to improve reproduction quality of the wobble signal, it is necessary to implement a measure, for example, such a contrivance as is disclosed in the patent document 1.